The treatment of various mineral substances by halogenated organosilanes is known in the art as described in the following U.S. Pat. Nos.: 2,722,504 (Fleck); 2,914,426 (Gaines); 3,963,627 (Cottrell); 4,175,159 (Raleigh); 4,183,980 (Nielsen); 4,214,914 (Ivanchev et al); and 4,255,489 (Nielsen) and Patent Numbers 321502 and 706371 of the Soviet Union.
Various attempts to treat and coat objects, including mineral particles, with halogenated organosilanes have met with various degrees of acceptability, but in the area of treating particulate mineral material, undesirable aspects remain to thwart maximum success. As an undesirable side reaction of the use of halogenated organosilanes is the evolution of gaseous hydrochloric acid in appreciable amounts. Usually this is taken care of by the use of wet scrubbers to absorb the gaseous hydrochloric acid, but a major problem exists in separating the acid gas from the particulate minerals. Attempts to remove the acid gas from the reaction chamber usually causes large amounts of the particulate mineral to be entrained which complicates separation of product and reduces yield. Furthermore, appreciabie amounts of unreacted silane is carried to the scrubber system where it belatedly reacts to form a tenacious, usually yellow, deposit throughout the system which requires frequent, costly, time-consuming cleanouts.
Efforts to eliminate the above problems and to improve product quality and yields were concentrated in the areas of different concentrations of the silane, varied reaction temperatures, increased reaction times, introduction into the reaction system of water as liquid or steam or both in an attempt to expedite the hydrolysis reaction with the silane and to increase overall efficiency. None of these efforts has been very successful nor have combinations of these efforts achieved a successful method essentially free of the problems set forth above.